What is the LHC?

The Large Hadron Collider, or LHC, is currently the worlds largest and most powerful particle accelerator, located in Switzerland/France (on the border near Geneva). The LHC consists of a 27 kilometer-long tunnel, at depths of up to 175 meters below the ground1 and is designed to collide protons at energies up to 14TeV at center of mass or heavy ions (mainly lead) at energies up to 5.5TeV (or close to 575TeV/nucleus). This specific type of collider is called a synchrotron, which basically means that it circulates two beams in opposite directions and then uses gigantic superconducting magnets located all the way around the ring to bend the beams.

Professor Brian Cox with the University of Manchester has a longer video here describing some of what they hope to find in more detail.

Expectations

The expectations of what exactly the Large Hadron Collider will find during its estimated lifetime are sky-high, and hopefully it will provide answers to some of the fundamental questions of the standard model of physics. This includes the hunt for the elusive Higgs boson(s) that is thought to give other particles their mass. The search for the Higgs boson (or the God-particle) has been one of the main objectives from the get-go and finding it would be vital for the continued support of Higgs mechanism for adding mass to particles. The paradox here is that not finding the Higgs boson(s) and thus not being able to prove the Higgs mechanism for adding mass to other particles could prove to be even more important to the evolution of physics, since it could in theory disprove the current standard model (and re-write it).

Potential discoveries

Here are some of the things LHC might find/confirm:

The Higgs boson(s)

The true properties of Quark-Gluon Plasma (QGP)

Proof for supersymmetry in nature (i.e. do all known particles have a supersymmetric partner?)

The existence of extra dimensions (predicted by string theory)

The nature of Dark matter

And so much more

Safety Review

The LHC Safety Assessment Group (LSAG) has continually reviewed the safety considerations of building and operating the LHC. The most recent report (2008) concludes that:

There is no basis for any concerns about the consequences of new particles or forms of matter that could possibly be produced by the LHC.2

Criticism

According to people like Walter L Wagner3 these aren't the only things the LHC might do. He, in company with a few other opponents, has gone to great lengths to stop the LHC because they claim that it will create microscopic black holes when started.

Has it already started colliding protons at record energies4? And no MBH's? Or have MBH's been created?

Microscopic black holes

People in general, and LHC-opponents in particular, seem to confuse these hypothetical microscopic black holes with the astronomical equivalent. That, however, is not in any way a valid comparison. The first flaw is that astronomical black holes are almost ridiculously massive while microscopic black holes are miniscule, and close to non-existent (I'll get back to that in a while). The second flaw with this comparison is the difference in how they accrete matter. Astronomical black holes accrete matter at an extreme rate and devour almost anything in their vicinity while microscopic black holes both (a) are far too small to accrete any matter whatsoever and (b) exist for far too short a time to be able to accrete any matter.

The general opinion is that the energies achieved at LHC are too low to be able to form microscopic black holes at all, but even so there are contradicting theories that suggest that microscopic black holes might be created even at these relatively low energies. These microscopic black holes are expected to evaporate almost instantly (of the order of $10^{-26}s$5) via something called Hawking radiation6 (also called black hole evaporation). The LSAG has even gone a step further and addressed the close to impossible scenario that MBH's are stable, and reached the following conclusion:

"Although theory predicts that microscopic black holes decay rapidly, even hypothetical stable black holes can be shown to be harmless by studying the consequences of their production by cosmic rays."7

"The fact that the Earth and Sun are still here rules out the possibility that cosmic rays or the LHC could produce dangerous charged microscopic black holes. If stable microscopic black holes had no electric charge, their interactions with the Earth would be very weak …The continued existence of such dense bodies, as well as the Earth, rules out the possibility of the LHC producing any dangerous black holes."8

The fact of the matter is that the actual MBH's that might "pop up" at LHC would be quite important for the evaluation/re-evaluation of Einstein's theory of relativity and whether Hawking radiation exists or not. If MBH's are created, that would more or less prove that there is at least one extra dimension and if that same MBH self-evaporates via Hawking radiation, it would prove that S. Hawking's theory is correct.

So there really is no reason whatsoever to fear the MBH's that most likely aren't even going to be created in the first place, and if created would be beyond harmless.

The whole MBH-scenario could be summed up as follows:

According to Einstein's theory MBH's shouldn't be created at the relatively low energies9 achieved at LHC.

It is however possible that a small extra dimension is available in the moment of the collision, in which case MBH's actually might be created.

These MBH's are expected to decay instantly thanks to this nifty little thing called Hawking radiation

Even if these MBH's don't decay instantly they don't pose any conceivable danger, since they would be too small to accrete any matter.

Strangelets

Strangelets are essentially an hypothetical particle that was first discussed as a possible threat from the RHIC at BNL10. The hypothesis states that Strangelets might be particles consisting of a bound state, which in this case means that there are several quarks puzzled together and thus behaves as a single unit (up, down and strange - approx. equal number). There's been quite a lot of fuzz from the LHC-opponents regarding this specific scenario and one might feel inclined to believe that this is some newfound cause for concern, but the truth is actually quite far from that. The Strangelet-scenario (or Ice-9) is actually, like many other claims, conveniently re-used from the anti-RHIC crowd and only minor changes in the formulas has been undertaken.

So why should we fear these Strangelets? Well, the theory predicts that negatively charged Strangelets produced at primarily RHIC, but even at LHC, possibly could be a quite nasty affair. Nasty in the way that negatively charged Strangelets are predicted to convert ordinary matter to strange matter at an exponentially increasing rate. Once the catalyst, or in this case a single negatively charged Strangelet, comes in contact with ordinary matter it will start to convert all of that ordinary matter to strange matter. Needless to say, that would leave us, the inhabitants of Earth, in a quite unfavorable situation. Or rather, Earth would be reduced to the size of a tennisball and all life as we know it would end almost instantaneously.

It sounds quite scary, doesn't it? Yes, but luckily it's just a theory with little to no basis in reality. Fact of the matter is that Strangelets, if they even exist, are expected to either (a) disintegrate so fast that they wouldn't have time to convert any matter to strange matter (thus harmless) or (b) be positively charged and thus have a repulsive effect on normal matter (yet again, harmless). Just like in the case with the MBH's this is just another harmless phenomena, that sadly have been mislabeled as a doomsday phenomena by the vocal LHC-opponents.

Furthermore, as of today there is no research whatsoever that indicates an increased risk of Strangelet production at LHC. Quite the opposite actually. According to LSAG, the likelihood of Strangelets being produced at LHC is actually reduced by several factors in respect to every single leap of energies (RHIC to LHC for ex.):

We conclude on general physical grounds that heavy-ion collisions at the LHC are less likely to produce strangelets than the lower-energy heavy-ion collisions already carried out in recent years at RHIC, just as strangelet production at RHIC was less likely than in previous lower-energy experiments carried out in the 1980s and 1990s11

Strangelets make up at least as good sci-fi scenarios as the MBH's but just like those, Strangelets remain just sci-fi. The fact of the matter is that searches for Strangelets have been carried out both in regards to cosmic rays and in regards to particle accelerators, without a single shred of evidence to talk about12.

Magnetic monopoles

Obviously neither microscopic black holes nor Strangelets are going to cause any spectacular disaster scenarios at LHC, but don't fret, there are plenty of more ways the LHC-opponents have "figured" out that earth might be destroyed. Take the case of the Magnetic monopoles for example. They are supposedly "particles with non-zero free magnetic charge"13. Just like strangelets the magnetic monopoles are purely theoretical and have not been observed. Since they haven't been observed there is no way to know whether or not they can exist at all. After all, empirical evidence like the continued existence of stellar bodies and our moon weighs far heavier than any theoretical reassurance will ever do.

Nevertheless, the theory predicts the magnetic monopoles to be quite a sturdy construction and is expected to be much greater in magnitude than the electric charge of electrons and protons. That is because any free magnetic charge is expected to be quantized and thereby much larger in magnitude than the aforementioned electric charge of electrons and protons. Because of these expected properties every search for magnetic monopoles have been focused on heavily-ionizing particles and quanta of magnetic charge. This search was carried out at RHIC and will be continued at LHC's heavy ion programme.

If you just look like magnetic monopoles according to the Standard model of physics you'll have a hard time making up any kind of doomsday scenario, but where's the fun in that?

It should be quite obvious at this point that the standard model of physics isn't all that favorable when it comes to supporting woo woo claims, so in order to create yet another scary scenario we simply have to look outside and beyond the standard model. By doing so one might come across the scary sibling of the harmless magnetic monopole; the nucleon decay catalyzing magnetic monopole. As the name implies, this novel particle causes nucleon decay by transforming protons and neutrons into electrons or positrons and unstable mesons14. Much like the negatively charged Strangelets this would cause a chain-reaction that would eventually ruin earth.

Fortunately, there are a few factors that talk against the creation of dangerous magnetic monopoles. The two main factors are:

A magnetic monopole possessing those properties is expected to weigh in on at least $10^{15}$GeV (or more) and thus couldn't possibly be created at the LHC.

And even if these estimates should be wrong, and a dangerous magnetic monopole was created, LSAG concludes that:

A quantitative discussion of the impact of such magnetic monopoles on Earth was presented in [1]15, where it was concluded that only a microgram of matter would be destroyed before the monopole exited the Earth. Independently of this conclusion, if monopoles could be produced by the LHC, high-energy cosmic rays would already have created many of them when striking the Earth and other astronomical bodies… …The continued existences of the Earth and other astronomical bodies such as the Sun mean that any magnetic monopoles produced by high-energy cosmic rays must be harmless. Likewise, if any monopoles are produced at the LHC, they will be harmless.

For some more information on this, see this brief article about why magnetic monopoles aren't likely to exist at all.

Thus we can rest assured that no dangerous magnetic monopoles will be created in LHC collisions.

Vacuum bubbles

When we talk about doomsday and the LHC there is one claim that weighs heavier than all the rest; the vacuum metastability event. Scientists have speculated that our current vacuum state isn't the most stable configuration, and that a violent enough collision (for example) could push us over into a more stable state, or a true vacuum. And certainly, such a transition would be most unfortunate for us, and actually the whole Universe as we know it. In fact, all life in the whole Universe would almost instantaneously cease to exist.

So why is this even a concern in regards to the LHC, when cosmic rays amongst others haven't been able to trigger such a phase transition during the whole existence of the Universe? The short answer is that it isn't, and actually has nothing to do with the LHC (but rather a hypothetical phenomena known as quantum tunneling). But even so, LSAG has to evaluate all risks, no matter how fringe they are.

The more elaborate answer is something along these lines; Since collisions at the LHC will have a center of mass-energy (COM) of up to 14TeV in p-p collisions (Protons) you could say that this is quite a big collision concentrated to a small space, the latter is one of many criteria that has to be fulfilled in order for a phase transition to happen (according to theories, that is). If a sufficiently extreme collision takes place at the aforementioned small space it might lead to the creation of a vacuum bubble. Such a vacuum bubble is then expected to propagate at the speed of light, thereby pushing us over to a new vacuum state and ending all life on earth instantaneously.

In other words, not a very good thing for us. This is however, fortunately, the least likely of all the proposed disaster scenarios and once again the observations of cosmic ray collisions many magnitudes greater than the GZK limit proves that the LHC isn't going to cause such a disaster. In fact, the theory that we even live in a false vacuum to begin with is very much discussed and no conclusive answer seems to be in sight. If it turns out that our current vacuum is the most stable configuration, then nothing in the Universe (and certainly not the LHC) is going to push us over to a new vacuum state. On the other hand, if it turns out that we actually do live in a false vacuum then we still can be 100% confident that the LHC isn't going to push us over to a more stable state, and most likely nothing else for that matter.

Why can we be sure of that? Because no collision that has taken place during the lifetime of our Universe has ever been able to cause a quantum tunneling, so the puny energies at the LHC couldn't possibly do that.

After all, everything the LHC does has already been done by the Universe, but now scientists get the chance to watch the collisions in realtime.

Related articles/videos

Footnotes

1. "The tunnel was built at a mean depth of 100 m, due to geological considerations …. Its depth varies between 175 m (under the Jura) and 50 m
(towards Lake Geneva)" [1][2]